1. Field of Invention
The invention relates generally to a method and system for modeling channel power, coordinating channel power information, and utilizing the coordinated channel power information as a basis for managing optical network elements in a multi-channel optical communications system.
2. Description of Related Art
Wavelength division multiplexing (WDM) has been used to increase the capacity of existing fiber optic networks. In a WDM system, plural optical signal channels are carried over a single optical fiber with each channel being assigned a particular wavelength. Such systems typically include a plurality of receivers, each detecting a respective channel by effectively filtering out the remaining channels.
Optical channels in a WDM system are frequently transmitted over silica based optical fibers, which typically have relatively low loss at wavelengths within a range of 1525 nm to 1580 nm. WDM optical signal channels at wavelengths within this low loss “window” can be transmitted over distances of approximately 50 km without significant attenuation. For distances beyond 50 km, however, optical amplifiers are used to compensate for optical fiber loss.
Typically, all of the channels of a WDM system are launched (transmitted or otherwise injected into an optical communications path) with the same power level. The flat power spectrum that results has certain advantages as in known in the art.
The advent of mixed channel plans where channels of different rates, data formats, channel spacings, etc are present in a WDM system has led the inventor to consider launching different channels at different power levels. The invention described in the parent application utilizes the fixed insertion losses present on different signal combining paths to impart a relative power difference between different bands of channels. In other words, one band of channels experiences a different amount of attenuation as it is combined with other bands of channels which may be accomplished by utilizing different optical signal combiners having different insertion losses for different bands of channels.
As discussed in the parent applications referenced above, the channel power values used for amplifier power control may be weighted (e.g. the power value of a channel may be an integer multiple of a defined channel unit power) to account for mixed channel plans. Specifically, the channel powers may be weighted according to the data rate and/or format of the signal. For example, a signal having a transmission rate of 2.5 Gbps may be used as a reference value with a weight of 1 channel unit; a signal having a 10 Gbps transmission rate using forward error correction may be weighted as 2 channel units; and a signal having a 10 Gbps transmission rate without forward error correction may be weighted as 4 channel units.
An optical amplifier according to the parent application could infer channel weighting values simply by knowing basic information about the signal such as data rate and format (e.g. FEC used or not), etc. The inferred channel weights are used to minimize ASE (amplified spontaneous emissions). Such a system, however, lacks granularity and uses fixed, predefined increments of signal attenuation and corresponding channel unit weightings. In other words, the inventor recognized that the basic concept of channel weighting could use refinement and could be extended to control points other than ASE minimization in an amplifier.